2-(3-Pyridinio)benzimidazolium pentachloridoantimonate(III) monohydrate

In the title compound, (C12H11N3)[SbCl5]·H2O, the SbIII centre is surrounded by five Cl atoms and displays a distorted square-pyramidal coordination geometry. The dihedral angle formed by the plane of the imidazole ring system with the pyridine ring is 4.380 (15)°. The crystal structure is stabilized by N—H⋯Cl, O—H⋯Cl and N—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title compound, (C 12 H 11 N 3 )[SbCl 5 ]ÁH 2 O, the Sb III centre is surrounded by five Cl atoms and displays a distorted square-pyramidal coordination geometry. The dihedral angle formed by the plane of the imidazole ring system with the pyridine ring is 4.380 (15) . The crystal structure is stabilized by N-HÁ Á ÁCl, O-HÁ Á ÁCl and N-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

S1. Comment
Benzimidazole and its derivatives have received great attention owing to their pharmacologic activities, such as antidiabetic (Minoura et al., 2004), antifungal (Pawar et al.,2004), and anticancer (Demirayak et al., 2002) activities. In this paper, the crystal structure of the title compound is reported.
The asymmetric unit of the title compound ( Fig. 1) contains a 2-(3′-pyridinio)benzimidazolium dication, a pentachloroantimonate dianion and a water molecule. In the anion, the antimony(III) atom is coordinated by five chloride anions in a distorted square-pyramidal geometry. The Sb-Cl distances are in the range 2.3687 (10)-2.7522 (11) Å. In the cation, the pyridine ring and the imidazole ring system are nearly coplanar, the dihedral angle they form being 4.360 (15) (Table 1), resulting in the formation of a three-dimensional network.

S2. Experimental
To a mixture of 2-(3′-pyridyl)benzimidazole (0.1 mmol) and water (7 ml), concentrated hydrochloric acid (12 M) was added dropwise till complete dissolution of the solid phase. Concentrated hydrochloric acid was similarly added dropwise to dissolve the solid phase persisting in a mixture of antimony trichloride (0.3 mmol) and water (7 ml). The two solutions were then mixed and stirred for 20 minutes. The resulting precipitate was filtered off and dissolved in hydrochloric acid. Colourless crystals suitable for X-ray analysis were formed after several weeks on slow evaporation of the solvent at room temperature.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq